/*
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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/*
 *
 *
 *
 *
 *
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain, as explained at
 * http://creativecommons.org/publicdomain/zero/1.0/
 */

package java.util.concurrent;

import java.util.*;

/**
 * A {@link Deque} that additionally supports blocking operations that wait
 * for the deque to become non-empty when retrieving an element, and wait for
 * space to become available in the deque when storing an element.
 *
 * <p>{@code BlockingDeque} methods come in four forms, with different ways
 * of handling operations that cannot be satisfied immediately, but may be
 * satisfied at some point in the future:
 * one throws an exception, the second returns a special value (either
 * {@code null} or {@code false}, depending on the operation), the third
 * blocks the current thread indefinitely until the operation can succeed,
 * and the fourth blocks for only a given maximum time limit before giving
 * up.  These methods are summarized in the following table:
 *
 * <table BORDER CELLPADDING=3 CELLSPACING=1>
 * <caption>Summary of BlockingDeque methods</caption>
 * <tr>
 * <td ALIGN=CENTER COLSPAN = 5> <b>First Element (Head)</b></td>
 * </tr>
 * <tr>
 * <td></td>
 * <td ALIGN=CENTER><em>Throws exception</em></td>
 * <td ALIGN=CENTER><em>Special value</em></td>
 * <td ALIGN=CENTER><em>Blocks</em></td>
 * <td ALIGN=CENTER><em>Times out</em></td>
 * </tr>
 * <tr>
 * <td><b>Insert</b></td>
 * <td>{@link #addFirst addFirst(e)}</td>
 * <td>{@link #offerFirst(Object) offerFirst(e)}</td>
 * <td>{@link #putFirst putFirst(e)}</td>
 * <td>{@link #offerFirst(Object, long, TimeUnit) offerFirst(e, time, unit)}</td>
 * </tr>
 * <tr>
 * <td><b>Remove</b></td>
 * <td>{@link #removeFirst removeFirst()}</td>
 * <td>{@link #pollFirst pollFirst()}</td>
 * <td>{@link #takeFirst takeFirst()}</td>
 * <td>{@link #pollFirst(long, TimeUnit) pollFirst(time, unit)}</td>
 * </tr>
 * <tr>
 * <td><b>Examine</b></td>
 * <td>{@link #getFirst getFirst()}</td>
 * <td>{@link #peekFirst peekFirst()}</td>
 * <td><em>not applicable</em></td>
 * <td><em>not applicable</em></td>
 * </tr>
 * <tr>
 * <td ALIGN=CENTER COLSPAN = 5> <b>Last Element (Tail)</b></td>
 * </tr>
 * <tr>
 * <td></td>
 * <td ALIGN=CENTER><em>Throws exception</em></td>
 * <td ALIGN=CENTER><em>Special value</em></td>
 * <td ALIGN=CENTER><em>Blocks</em></td>
 * <td ALIGN=CENTER><em>Times out</em></td>
 * </tr>
 * <tr>
 * <td><b>Insert</b></td>
 * <td>{@link #addLast addLast(e)}</td>
 * <td>{@link #offerLast(Object) offerLast(e)}</td>
 * <td>{@link #putLast putLast(e)}</td>
 * <td>{@link #offerLast(Object, long, TimeUnit) offerLast(e, time, unit)}</td>
 * </tr>
 * <tr>
 * <td><b>Remove</b></td>
 * <td>{@link #removeLast() removeLast()}</td>
 * <td>{@link #pollLast() pollLast()}</td>
 * <td>{@link #takeLast takeLast()}</td>
 * <td>{@link #pollLast(long, TimeUnit) pollLast(time, unit)}</td>
 * </tr>
 * <tr>
 * <td><b>Examine</b></td>
 * <td>{@link #getLast getLast()}</td>
 * <td>{@link #peekLast peekLast()}</td>
 * <td><em>not applicable</em></td>
 * <td><em>not applicable</em></td>
 * </tr>
 * </table>
 *
 * <p>Like any {@link BlockingQueue}, a {@code BlockingDeque} is thread safe,
 * does not permit null elements, and may (or may not) be
 * capacity-constrained.
 *
 * <p>A {@code BlockingDeque} implementation may be used directly as a FIFO
 * {@code BlockingQueue}. The methods inherited from the
 * {@code BlockingQueue} interface are precisely equivalent to
 * {@code BlockingDeque} methods as indicated in the following table:
 *
 * <table BORDER CELLPADDING=3 CELLSPACING=1>
 * <caption>Comparison of BlockingQueue and BlockingDeque methods</caption>
 * <tr>
 * <td ALIGN=CENTER> <b>{@code BlockingQueue} Method</b></td>
 * <td ALIGN=CENTER> <b>Equivalent {@code BlockingDeque} Method</b></td>
 * </tr>
 * <tr>
 * <td ALIGN=CENTER COLSPAN = 2> <b>Insert</b></td>
 * </tr>
 * <tr>
 * <td>{@link #add(Object) add(e)}</td>
 * <td>{@link #addLast(Object) addLast(e)}</td>
 * </tr>
 * <tr>
 * <td>{@link #offer(Object) offer(e)}</td>
 * <td>{@link #offerLast(Object) offerLast(e)}</td>
 * </tr>
 * <tr>
 * <td>{@link #put(Object) put(e)}</td>
 * <td>{@link #putLast(Object) putLast(e)}</td>
 * </tr>
 * <tr>
 * <td>{@link #offer(Object, long, TimeUnit) offer(e, time, unit)}</td>
 * <td>{@link #offerLast(Object, long, TimeUnit) offerLast(e, time, unit)}</td>
 * </tr>
 * <tr>
 * <td ALIGN=CENTER COLSPAN = 2> <b>Remove</b></td>
 * </tr>
 * <tr>
 * <td>{@link #remove() remove()}</td>
 * <td>{@link #removeFirst() removeFirst()}</td>
 * </tr>
 * <tr>
 * <td>{@link #poll() poll()}</td>
 * <td>{@link #pollFirst() pollFirst()}</td>
 * </tr>
 * <tr>
 * <td>{@link #take() take()}</td>
 * <td>{@link #takeFirst() takeFirst()}</td>
 * </tr>
 * <tr>
 * <td>{@link #poll(long, TimeUnit) poll(time, unit)}</td>
 * <td>{@link #pollFirst(long, TimeUnit) pollFirst(time, unit)}</td>
 * </tr>
 * <tr>
 * <td ALIGN=CENTER COLSPAN = 2> <b>Examine</b></td>
 * </tr>
 * <tr>
 * <td>{@link #element() element()}</td>
 * <td>{@link #getFirst() getFirst()}</td>
 * </tr>
 * <tr>
 * <td>{@link #peek() peek()}</td>
 * <td>{@link #peekFirst() peekFirst()}</td>
 * </tr>
 * </table>
 *
 * <p>Memory consistency effects: As with other concurrent
 * collections, actions in a thread prior to placing an object into a
 * {@code BlockingDeque}
 * <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
 * actions subsequent to the access or removal of that element from
 * the {@code BlockingDeque} in another thread.
 *
 * <p>This interface is a member of the
 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
 * Java Collections Framework</a>.
 *
 * @param <E> the type of elements held in this collection
 * @author Doug Lea
 * @since 1.6
 */
public interface BlockingDeque<E> extends BlockingQueue<E>, Deque<E> {
    /*
     * We have "diamond" multiple interface inheritance here, and that
     * introduces ambiguities.  Methods might end up with different
     * specs depending on the branch chosen by javadoc.  Thus a lot of
     * methods specs here are copied from superinterfaces.
     */

  /**
   * Inserts the specified element at the front of this deque if it is
   * possible to do so immediately without violating capacity restrictions,
   * throwing an {@code IllegalStateException} if no space is currently
   * available.  When using a capacity-restricted deque, it is generally
   * preferable to use {@link #offerFirst(Object) offerFirst}.
   *
   * @param e the element to add
   * @throws IllegalStateException {@inheritDoc}
   * @throws ClassCastException {@inheritDoc}
   * @throws NullPointerException if the specified element is null
   * @throws IllegalArgumentException {@inheritDoc}
   */
  void addFirst(E e);

  /**
   * Inserts the specified element at the end of this deque if it is
   * possible to do so immediately without violating capacity restrictions,
   * throwing an {@code IllegalStateException} if no space is currently
   * available.  When using a capacity-restricted deque, it is generally
   * preferable to use {@link #offerLast(Object) offerLast}.
   *
   * @param e the element to add
   * @throws IllegalStateException {@inheritDoc}
   * @throws ClassCastException {@inheritDoc}
   * @throws NullPointerException if the specified element is null
   * @throws IllegalArgumentException {@inheritDoc}
   */
  void addLast(E e);

  /**
   * Inserts the specified element at the front of this deque if it is
   * possible to do so immediately without violating capacity restrictions,
   * returning {@code true} upon success and {@code false} if no space is
   * currently available.
   * When using a capacity-restricted deque, this method is generally
   * preferable to the {@link #addFirst(Object) addFirst} method, which can
   * fail to insert an element only by throwing an exception.
   *
   * @param e the element to add
   * @throws ClassCastException {@inheritDoc}
   * @throws NullPointerException if the specified element is null
   * @throws IllegalArgumentException {@inheritDoc}
   */
  boolean offerFirst(E e);

  /**
   * Inserts the specified element at the end of this deque if it is
   * possible to do so immediately without violating capacity restrictions,
   * returning {@code true} upon success and {@code false} if no space is
   * currently available.
   * When using a capacity-restricted deque, this method is generally
   * preferable to the {@link #addLast(Object) addLast} method, which can
   * fail to insert an element only by throwing an exception.
   *
   * @param e the element to add
   * @throws ClassCastException {@inheritDoc}
   * @throws NullPointerException if the specified element is null
   * @throws IllegalArgumentException {@inheritDoc}
   */
  boolean offerLast(E e);

  /**
   * Inserts the specified element at the front of this deque,
   * waiting if necessary for space to become available.
   *
   * @param e the element to add
   * @throws InterruptedException if interrupted while waiting
   * @throws ClassCastException if the class of the specified element prevents it from being added
   * to this deque
   * @throws NullPointerException if the specified element is null
   * @throws IllegalArgumentException if some property of the specified element prevents it from
   * being added to this deque
   */
  void putFirst(E e) throws InterruptedException;

  /**
   * Inserts the specified element at the end of this deque,
   * waiting if necessary for space to become available.
   *
   * @param e the element to add
   * @throws InterruptedException if interrupted while waiting
   * @throws ClassCastException if the class of the specified element prevents it from being added
   * to this deque
   * @throws NullPointerException if the specified element is null
   * @throws IllegalArgumentException if some property of the specified element prevents it from
   * being added to this deque
   */
  void putLast(E e) throws InterruptedException;

  /**
   * Inserts the specified element at the front of this deque,
   * waiting up to the specified wait time if necessary for space to
   * become available.
   *
   * @param e the element to add
   * @param timeout how long to wait before giving up, in units of {@code unit}
   * @param unit a {@code TimeUnit} determining how to interpret the {@code timeout} parameter
   * @return {@code true} if successful, or {@code false} if the specified waiting time elapses
   * before space is available
   * @throws InterruptedException if interrupted while waiting
   * @throws ClassCastException if the class of the specified element prevents it from being added
   * to this deque
   * @throws NullPointerException if the specified element is null
   * @throws IllegalArgumentException if some property of the specified element prevents it from
   * being added to this deque
   */
  boolean offerFirst(E e, long timeout, TimeUnit unit)
      throws InterruptedException;

  /**
   * Inserts the specified element at the end of this deque,
   * waiting up to the specified wait time if necessary for space to
   * become available.
   *
   * @param e the element to add
   * @param timeout how long to wait before giving up, in units of {@code unit}
   * @param unit a {@code TimeUnit} determining how to interpret the {@code timeout} parameter
   * @return {@code true} if successful, or {@code false} if the specified waiting time elapses
   * before space is available
   * @throws InterruptedException if interrupted while waiting
   * @throws ClassCastException if the class of the specified element prevents it from being added
   * to this deque
   * @throws NullPointerException if the specified element is null
   * @throws IllegalArgumentException if some property of the specified element prevents it from
   * being added to this deque
   */
  boolean offerLast(E e, long timeout, TimeUnit unit)
      throws InterruptedException;

  /**
   * Retrieves and removes the first element of this deque, waiting
   * if necessary until an element becomes available.
   *
   * @return the head of this deque
   * @throws InterruptedException if interrupted while waiting
   */
  E takeFirst() throws InterruptedException;

  /**
   * Retrieves and removes the last element of this deque, waiting
   * if necessary until an element becomes available.
   *
   * @return the tail of this deque
   * @throws InterruptedException if interrupted while waiting
   */
  E takeLast() throws InterruptedException;

  /**
   * Retrieves and removes the first element of this deque, waiting
   * up to the specified wait time if necessary for an element to
   * become available.
   *
   * @param timeout how long to wait before giving up, in units of {@code unit}
   * @param unit a {@code TimeUnit} determining how to interpret the {@code timeout} parameter
   * @return the head of this deque, or {@code null} if the specified waiting time elapses before an
   * element is available
   * @throws InterruptedException if interrupted while waiting
   */
  E pollFirst(long timeout, TimeUnit unit)
      throws InterruptedException;

  /**
   * Retrieves and removes the last element of this deque, waiting
   * up to the specified wait time if necessary for an element to
   * become available.
   *
   * @param timeout how long to wait before giving up, in units of {@code unit}
   * @param unit a {@code TimeUnit} determining how to interpret the {@code timeout} parameter
   * @return the tail of this deque, or {@code null} if the specified waiting time elapses before an
   * element is available
   * @throws InterruptedException if interrupted while waiting
   */
  E pollLast(long timeout, TimeUnit unit)
      throws InterruptedException;

  /**
   * Removes the first occurrence of the specified element from this deque.
   * If the deque does not contain the element, it is unchanged.
   * More formally, removes the first element {@code e} such that
   * {@code o.equals(e)} (if such an element exists).
   * Returns {@code true} if this deque contained the specified element
   * (or equivalently, if this deque changed as a result of the call).
   *
   * @param o element to be removed from this deque, if present
   * @return {@code true} if an element was removed as a result of this call
   * @throws ClassCastException if the class of the specified element is incompatible with this
   * deque (<a href="../Collection.html#optional-restrictions">optional</a>)
   * @throws NullPointerException if the specified element is null (<a
   * href="../Collection.html#optional-restrictions">optional</a>)
   */
  boolean removeFirstOccurrence(Object o);

  /**
   * Removes the last occurrence of the specified element from this deque.
   * If the deque does not contain the element, it is unchanged.
   * More formally, removes the last element {@code e} such that
   * {@code o.equals(e)} (if such an element exists).
   * Returns {@code true} if this deque contained the specified element
   * (or equivalently, if this deque changed as a result of the call).
   *
   * @param o element to be removed from this deque, if present
   * @return {@code true} if an element was removed as a result of this call
   * @throws ClassCastException if the class of the specified element is incompatible with this
   * deque (<a href="../Collection.html#optional-restrictions">optional</a>)
   * @throws NullPointerException if the specified element is null (<a
   * href="../Collection.html#optional-restrictions">optional</a>)
   */
  boolean removeLastOccurrence(Object o);

  // *** BlockingQueue methods ***

  /**
   * Inserts the specified element into the queue represented by this deque
   * (in other words, at the tail of this deque) if it is possible to do so
   * immediately without violating capacity restrictions, returning
   * {@code true} upon success and throwing an
   * {@code IllegalStateException} if no space is currently available.
   * When using a capacity-restricted deque, it is generally preferable to
   * use {@link #offer(Object) offer}.
   *
   * <p>This method is equivalent to {@link #addLast(Object) addLast}.
   *
   * @param e the element to add
   * @throws IllegalStateException {@inheritDoc}
   * @throws ClassCastException if the class of the specified element prevents it from being added
   * to this deque
   * @throws NullPointerException if the specified element is null
   * @throws IllegalArgumentException if some property of the specified element prevents it from
   * being added to this deque
   */
  boolean add(E e);

  /**
   * Inserts the specified element into the queue represented by this deque
   * (in other words, at the tail of this deque) if it is possible to do so
   * immediately without violating capacity restrictions, returning
   * {@code true} upon success and {@code false} if no space is currently
   * available.  When using a capacity-restricted deque, this method is
   * generally preferable to the {@link #add} method, which can fail to
   * insert an element only by throwing an exception.
   *
   * <p>This method is equivalent to {@link #offerLast(Object) offerLast}.
   *
   * @param e the element to add
   * @throws ClassCastException if the class of the specified element prevents it from being added
   * to this deque
   * @throws NullPointerException if the specified element is null
   * @throws IllegalArgumentException if some property of the specified element prevents it from
   * being added to this deque
   */
  boolean offer(E e);

  /**
   * Inserts the specified element into the queue represented by this deque
   * (in other words, at the tail of this deque), waiting if necessary for
   * space to become available.
   *
   * <p>This method is equivalent to {@link #putLast(Object) putLast}.
   *
   * @param e the element to add
   * @throws InterruptedException {@inheritDoc}
   * @throws ClassCastException if the class of the specified element prevents it from being added
   * to this deque
   * @throws NullPointerException if the specified element is null
   * @throws IllegalArgumentException if some property of the specified element prevents it from
   * being added to this deque
   */
  void put(E e) throws InterruptedException;

  /**
   * Inserts the specified element into the queue represented by this deque
   * (in other words, at the tail of this deque), waiting up to the
   * specified wait time if necessary for space to become available.
   *
   * <p>This method is equivalent to
   * {@link #offerLast(Object, long, TimeUnit) offerLast}.
   *
   * @param e the element to add
   * @return {@code true} if the element was added to this deque, else {@code false}
   * @throws InterruptedException {@inheritDoc}
   * @throws ClassCastException if the class of the specified element prevents it from being added
   * to this deque
   * @throws NullPointerException if the specified element is null
   * @throws IllegalArgumentException if some property of the specified element prevents it from
   * being added to this deque
   */
  boolean offer(E e, long timeout, TimeUnit unit)
      throws InterruptedException;

  /**
   * Retrieves and removes the head of the queue represented by this deque
   * (in other words, the first element of this deque).
   * This method differs from {@link #poll poll} only in that it
   * throws an exception if this deque is empty.
   *
   * <p>This method is equivalent to {@link #removeFirst() removeFirst}.
   *
   * @return the head of the queue represented by this deque
   * @throws NoSuchElementException if this deque is empty
   */
  E remove();

  /**
   * Retrieves and removes the head of the queue represented by this deque
   * (in other words, the first element of this deque), or returns
   * {@code null} if this deque is empty.
   *
   * <p>This method is equivalent to {@link #pollFirst()}.
   *
   * @return the head of this deque, or {@code null} if this deque is empty
   */
  E poll();

  /**
   * Retrieves and removes the head of the queue represented by this deque
   * (in other words, the first element of this deque), waiting if
   * necessary until an element becomes available.
   *
   * <p>This method is equivalent to {@link #takeFirst() takeFirst}.
   *
   * @return the head of this deque
   * @throws InterruptedException if interrupted while waiting
   */
  E take() throws InterruptedException;

  /**
   * Retrieves and removes the head of the queue represented by this deque
   * (in other words, the first element of this deque), waiting up to the
   * specified wait time if necessary for an element to become available.
   *
   * <p>This method is equivalent to
   * {@link #pollFirst(long, TimeUnit) pollFirst}.
   *
   * @return the head of this deque, or {@code null} if the specified waiting time elapses before an
   * element is available
   * @throws InterruptedException if interrupted while waiting
   */
  E poll(long timeout, TimeUnit unit)
      throws InterruptedException;

  /**
   * Retrieves, but does not remove, the head of the queue represented by
   * this deque (in other words, the first element of this deque).
   * This method differs from {@link #peek peek} only in that it throws an
   * exception if this deque is empty.
   *
   * <p>This method is equivalent to {@link #getFirst() getFirst}.
   *
   * @return the head of this deque
   * @throws NoSuchElementException if this deque is empty
   */
  E element();

  /**
   * Retrieves, but does not remove, the head of the queue represented by
   * this deque (in other words, the first element of this deque), or
   * returns {@code null} if this deque is empty.
   *
   * <p>This method is equivalent to {@link #peekFirst() peekFirst}.
   *
   * @return the head of this deque, or {@code null} if this deque is empty
   */
  E peek();

  /**
   * Removes the first occurrence of the specified element from this deque.
   * If the deque does not contain the element, it is unchanged.
   * More formally, removes the first element {@code e} such that
   * {@code o.equals(e)} (if such an element exists).
   * Returns {@code true} if this deque contained the specified element
   * (or equivalently, if this deque changed as a result of the call).
   *
   * <p>This method is equivalent to
   * {@link #removeFirstOccurrence(Object) removeFirstOccurrence}.
   *
   * @param o element to be removed from this deque, if present
   * @return {@code true} if this deque changed as a result of the call
   * @throws ClassCastException if the class of the specified element is incompatible with this
   * deque (<a href="../Collection.html#optional-restrictions">optional</a>)
   * @throws NullPointerException if the specified element is null (<a
   * href="../Collection.html#optional-restrictions">optional</a>)
   */
  boolean remove(Object o);

  /**
   * Returns {@code true} if this deque contains the specified element.
   * More formally, returns {@code true} if and only if this deque contains
   * at least one element {@code e} such that {@code o.equals(e)}.
   *
   * @param o object to be checked for containment in this deque
   * @return {@code true} if this deque contains the specified element
   * @throws ClassCastException if the class of the specified element is incompatible with this
   * deque (<a href="../Collection.html#optional-restrictions">optional</a>)
   * @throws NullPointerException if the specified element is null (<a
   * href="../Collection.html#optional-restrictions">optional</a>)
   */
  public boolean contains(Object o);

  /**
   * Returns the number of elements in this deque.
   *
   * @return the number of elements in this deque
   */
  public int size();

  /**
   * Returns an iterator over the elements in this deque in proper sequence.
   * The elements will be returned in order from first (head) to last (tail).
   *
   * @return an iterator over the elements in this deque in proper sequence
   */
  Iterator<E> iterator();

  // *** Stack methods ***

  /**
   * Pushes an element onto the stack represented by this deque (in other
   * words, at the head of this deque) if it is possible to do so
   * immediately without violating capacity restrictions, throwing an
   * {@code IllegalStateException} if no space is currently available.
   *
   * <p>This method is equivalent to {@link #addFirst(Object) addFirst}.
   *
   * @throws IllegalStateException {@inheritDoc}
   * @throws ClassCastException {@inheritDoc}
   * @throws NullPointerException if the specified element is null
   * @throws IllegalArgumentException {@inheritDoc}
   */
  void push(E e);
}
